1. Field of the Invention
The present invention relates generally to a weaving loom and more specifically to a circuit arrangement for a shuttleless weaving loom which facilitates accurate weft yarn dispensing.
2. Description of the Prior Art
A previously proposed weft yarn storage-supply arrangement for a weaving loom is shown in FIG. 1 of the drawings. In this arrangement weft yarn y is wound onto a drum 2 by a winding arrangement 3 and retained thereon by a retaining device 4. During picking the retaining device 4 is actuated to retract a blocking member 5 from a recess 6 formed in the drum 2 and permit a number of loops of weft yarn y to drawn axially off the drum. The amount of yarn y stored on the drum is controlled by a first sensor 7 which directs a beam of light against the drum and which, in response to the amount of light reflected therefrom, induces suitable energization of the winding arrangement 3 in a manner to maintain a predetermined length of yarn on the drum. The amount of yarn permitted to be released from the drum 2 during each picking operation is controlled by a second sensor 8 which, like the first, directs a beam of light against the drum 2 in a manner that the passage of weft yarn y across the point where the beam impinges on the drum 2, induces a change in the amount of light reflected and thus the output of the light receiving section of the second sensor 8. A control unit 9 is responsive to the output of the second sensor 8 and controls the operation of the retaining device 4.
However, the latter mentioned sensor arrangement has suffered from the drawback that when applied to high speed weaving machines wherein weft yarns having a diameter ranging from tens of microns to hundreds of microns, are exposed to the beam of light for only a few micro seconds, accurate detection of every loop being drawn off the drum becomes extremely difficult. Non-detection of one of more loops of weft yarn y being off the storage drum 4 of course invites an inevitable malfunction of the loom.
Further with this arrangement, even though the time for which the weft yarn is drawn off the storage drum arrangement is closely related to the actual weaving phase, the weft yarn withdrawing speed varies with the injection pressure, width of the fabric being woven, the type of thread being picked the speed at which the loom is being operated, etc., rendering it impossible to automatically set the thread retaining device actuation timing based on a predetermined weft yarn withdrawing speed. Viz., implementation of this type of control leads to the situation wherein the retaining device 4 tends to be actuated either too early or too late.
A full description of the above mentioned arrangement may be found in Japanese Patent Application Provisional publication No. Sho 57-29640 or corresponding U.S. Pat. No. 4,407,336 issued in the name of Steiner on Oct. 4, 1983.